Re: [Qemu-devel] [patch] make PCI work with Windows NT 4 guest

[Ben Pfaff <blp@cs.stanford.edu>]

Johannes Schindelin <Johannes.Schindelin@gmx.de> writes:

> great work! Out of curiosity: how did you manage to find out what is going
> wrong? (may help others to debug similarly complicated situations...)

To tell that the lack of CMOS was a problem, I tried the WNT4
install under both Bochs (in which WNT4 worked) and qemu and set
up both to dump out IDE port reads and writes in the same trace
format.  Then I `diff'ed the outputs.  There were lots of
differences so I adjusted the qemu state machine until the traces
were bug-for-bug identical.  It still didn't work so I knew
something else had to be the problem, and eventually I thought of
the CMOS.

I did about the same thing for figuring out how to make PCI work.
I turned on lots of debug print statements, then ran installs
with PCI enabled and disabled, and looked at the `diff' between
the debug print outputs.  There was a particular point in the PCI
trace where the guest was sitting in a loop polling the IDE
status register until it timed out, so I figured that it was
looking for a bit that wasn't on.  Adding the "seek complete" bit
fixed it.
-- 
"...I've forgotten where I was going with this,
 but you can bet it was scathing."
--DesiredUsername